For radiotherapy treatments, plans are made based on previously-captured perspective images of a patient so that a focus of a disease in the body of the patient is precisely irradiated. An irradiation direction, an irradiation strength, and the like, are predetermined when a plan is made.
There are positioning apparatuses and methods for aligning a position, at the planning time, of a radiographic referential image of an object to be irradiated, to a position of the object at the time of actual irradiation. Conventionally, there is technology of displaying a guideline based on the epipolar geometry when a positioning process is performed. However, it is difficult to precisely designate, using a display image with low resolution, positions of points to be used for the positioning process.